PXIE progress: LEBT successfully delivers maximum current

Lionel Prost of the Accelerator Division inspects the PXIE low-energy beam transport, which is now capable of delivering 10 milliamps of current. Photo: Reidar Hahn

Fermilab has paved the first few feet of the long road to a dramatic upgrade of its injection complex. Specifically, it's 8 feet, the current length of PXIE, a test accelerator that prototypes the front end of the proposed upgrades known as PIP-II.

The project accomplished a significant step when researchers recently passed beam through the nearly complete low-energy beam transport with a current of 10 milliamps, PIP-II's specifications.

"Meeting the specification is the result of the hard work of many people," said Paul Derwent, head of the PIP-II Department within the Accelerator Division.

An important goal was to pass this current through the LEBT with losses of less than 10 percent. The PXIE team has achieved that with losses of less than two percent.

PXIE's LEBT is a series of components that links a negative hydrogen ion source to a radio-frequency quadrupole, the beam's first accelerating component. The LEBT focuses, shapes and directs a nominal 5-milliamp beam so as to fit the size, position and angle requirements for the RFQ. After achieving the 10-milliamp milestone, the PXIE research team now concentrates its efforts on other beam characteristics related to beam quality. Poor beam quality would lead to beam loss downstream, which in turn can cause a loss of superconductivity in a cryogenic section of the future accelerator.

Lionel Prost, lead scientist for the ion source and LEBT portions of PXIE, said that even though LEBTs are not new technology, building one is no small task.

Dozens of people from all over Fermilab have contributed to designing, building and commissioning the LEBT. Additional support came from Oak Ridge National Laboratory's Spallation Neutron Source and Lawrence Berkeley National Laboratory, which made contributions to the LEBT design and beam instrumentation. Berkeley Lab is also building the RFQ, which is expected to be completed in the spring.

The final goal of PXIE is to address technical risks associated with the PIP-II plans and help establish a reliable budget for the full-scale project.

"The theory and the machine itself are not the same thing," Prost explained. "You have to make it work. So you take measurements, analyze the data and try to figure out why it does not match your expectations — and repeat until you understand what you actually have in front of you rather than what you had drawn up!"

Ultimately, PXIE will accelerate negative hydrogen ions to 25 million electronvolts. The ions will be carefully packed in a complicated sequence of bunches, allowing the future accelerator to feed multiple experiments simultaneously.

PXIE, designed to operate as a continuous-wave machine, will also demonstrate pulsed-beam operation required for injection into the Booster.

The road ahead is long, but the first few feet look to be on solid ground.

—Troy Rummler

In Brief

State Representative Linda Chapa LaVia visits Fermilab

State Representative Linda Chapa LaVia, left, is greeted in the Wilson Hall atrium by (left to right) Katie Yurkewicz, head of the Office of Communication; Mike Weis, head of the DOE Fermi Site Office; and Randy Ortgiesen, head of the Office of Campus Strategy and Readiness. Photo: Reidar Hahn

State Representative Linda Chapa LaVia visited Fermilab on Wednesday with four members of her district office staff. The group toured Wilson Hall, got a behind-the-scenes look at the IARC building and visited the underground neutrino cavern. Chapa LaVia represents the 83rd district and spoke with lab staffers about science and the lab's educational outreach.

Death

In memoriam: Walter Limbaugh

Fermilab retiree Walter Limbaugh passed away on Dec. 18. He worked as a welder at the laboratory from 1970 to 1989.

A visitation for Limbaugh will be held on Sunday, Dec. 21, from 4-7 p.m. at Moss Family Funeral Home, 209 South Batavia Avenue in Batavia. Funeral services will be held at the funeral home on Monday, Dec. 22, at 10 a.m. Internment will follow in River Hills Memorial Park.

Comet landing named Physics World 2014 Breakthrough of the Year

From Physics World, Dec. 12, 2014

The Physics World 2014 Breakthrough of the Year goes to ESA's Rosetta mission for being the first to land a spacecraft on a comet. Nine other achievements are highly commended and cover topics ranging from nuclear physics to acoustics.

Measuring extra dimensions

A branch that is one-dimensional to a chameleon is two-dimensional to an ant, and particles or waves that travel along the short dimension can loop around and even resonate.

Perhaps the most surprising thing about the LHC is that it has the potential to discover new dimensions. This is strange because dimensions are mutually perpendicular directions, like length, width and height — a new dimension would be a direction that is perpendicular to all three. Not only is it hard to believe that such a thing could have gone unnoticed until now, but how could colliding protons reveal it?

If a fourth dimension (not counting time) were exactly like length, width and height, we would have always known about it. We would describe the size of a box with four numbers, rather than three. When physicists speak of "extra dimensions," they mean one or more dimensions that do not affect our macroscopic world, either because we're stuck to a three-dimensional slice of the larger-dimensional space or because the extra dimension loops back on itself: If you travel far enough along it, you end up where you started, and "far enough" is a fraction of a proton's width.

In one popular theory, both effects are responsible for hiding extra dimensions. The dimensions are small, and all particles are stuck to our three-dimensional slice except gravitons. This theory could explain why gravity is so weak compared to electromagnetism and nuclear forces — most gravitons would be lost in the extra dimensions.

In such a scenario, colliding protons would reveal the extra dimensions by creating a resonance of gravitons spinning around the extra dimensions. That is, the collision would create gravitons that go into the extra dimensions, loop around them, and arrive where they started. At the right energy, the gravitons would resonate like a ringing bell. The final result of this resonance would be to produce more particles, which can be observed by a detector like CMS.

The problem is that ordinary collisions also produce lots of particles: How would ordinary particle production be distinguished from extra dimensions? A group of CMS scientists approached the problem by measuring angular distributions of the observed particles, since extra dimensions would produce a different angular distribution than ordinary collisions. In fact, these scientists also used the angular distribution to determine if quarks, the constituents of protons, are themselves made of smaller particles.

The result was that no extra dimensions or quark substructure was seen, at scales that are 10 thousand times smaller than a proton's radius.

—Jim Pivarski

These physicists contributed to this paper.

Patricia McBride is leaving her position as U.S. CMS project manager to run the Fermilab Particle Physics Division. She will be replaced by Fermilab scientist Lothar Bauerdick. Thanks, Patty, and good luck in your new position. Welcome, Lothar!

Photo of the Day

Mooselighting

... because 'Chrisbison' just doesn't have the same ring. You can see Julie Kurnat's chalk drawing in ICB trailer 157. Image: Julie Kurnat, TD

In Brief

Science Next Door January newsletter now online

The January edition of "Science Next Door," Fermilab's monthly community newsletter, is now available online. View it or subscribe to get the latest about the laboratory's public events, including tours, lectures, arts events and volunteer opportunities.